Field of the Invention
The present disclosure relates to control of an image formation apparatus and particularly to control of an image formation apparatus of an electrophotography type.
Description of the Related Art
An image formation apparatus of an electrophotography type has widely been used. The image formation, apparatus of the electrophotography type performs, as print processing, evenly charging a photoconductor, forming an electrostatic latent image by exposing the photoconductor, attaching toner to the electrostatic latent image on the photoconductor, primarily transferring a toner image on the photoconductor to a transfer belt, secondarily transferring the toner image on the transfer belt to a sheet (for example, printing paper), and fixing the toner image to a sheet by using a fixation apparatus.
The fixation apparatus is constituted of a fixation roller and a pressurization roller. A heater is provided in the fixation roller. The image formation apparatus drives the heater so as to heat the fixation roller and presses the conveyed sheet against the fixation roller with the pressurization roller. The toner image is thus molten and fixed onto the sheet.
In order to prevent wrinkles from being produced in a sheet in the fixation apparatus, tensile force should be applied to the sheet while the sheet is passing between the fixation apparatus and a secondary transfer portion. To that end, the fixation roller is controlled, for example, to be higher in speed of conveyance approximately by 0.2% than the secondary transfer portion. The sheet is thus pulled by the fixation roller and tensile force is applied to the sheet.
When printing is performed while tensile force is applied to the sheet, however, a diameter of the fixation roller increases due to thermal expansion and a speed of conveyance of the fixation roller increases. With increase in speed of conveyance by the fixation roller, a difference in speed of conveyance between the fixation roller and the secondary transfer portion increases and misalignment in transfer in the secondary transfer portion occurs. Misalignment in transfer results in misalignment of colors.
In connection with a technique for solving this problem, Japanese Laid-Open Patent Publication No. 2010-55064 discloses a speed detection-apparatus for “detecting velocity fluctuation of a moving member in a simple manner with high accuracy.” The speed detection apparatus obtains an image pattern at a constant time interval during movement of the moving member and calculates a speed of the moving member based on the obtained image pattern. When change in speed is sensed, the speed detection apparatus adjusts a speed of a fixation roller. A difference in speed between the fixation roller and the secondary transfer portion is thus suppressed.
The fixation roller may be eccentric and rotation of the fixation roller may not be stable. When rotation of the fixation roller is not stable, a sheet flutters during conveyance. The speed detection apparatus disclosed in Japanese Laid-Open Patent Publication No. 2010-55064 calculates a speed of a sheet based on a plurality of images obtained by shooting the sheet at a constant interval. When the sheet flutters during conveyance, a size of the sheet in the image fluctuates. Consequently, the speed detection apparatus cannot accurately calculate a speed of the moving member. Therefore, an image formation apparatus which can accurately sense a speed of conveyance of a moving element such as a sheet even when the moving element flutters during conveyance is desired.